This invention relates to receipt and processing of light signals by electronic apparatus associated with the eye.
Diseases of, or damage to, the eye, such as macular degeneration and retinitis pigmentosa, often interfere with normal sight by compromising or destroying one or two components of the eye and leaving other components relatively untouched. Where this occurs, normal sight in an eye might be restored by providing a mechanism that provides an action equivalent to that of the compromised or destroyed component(s) and thereby restores overall functionality of the eye. However, application of this approach to the eye has proved hard to achieve, because of the nature of the components whose action must be restored and because the mechanism must be compatible with, but not interfere with, the eye""s normal operation.
What is needed is an approach that provides an alternate path for light signal sensing on a pixel-size scale and that is small enough to be fitted within, or adjacent to, the compromised eye. Preferably, the approach should provide wavelength-sensitive light signal processing and should be flexible enough to allow signal processing changes that account for a changed visual environment. In addition, the approach should also allow analyses to improve an understanding of the eye""s processing and integration of light signals, as well as changes in the processing and integration functions that may occur in response to diseases and other environmental perturbations.
These needs are met by the invention, which provides a system that receives, and identifies the site of receipt of, light on a pixel-size scale, delivers an electrical signal indicating this localized receipt of the light to an active layer of a subject""s eye that normally receives and processes such localized signals, and thereafter utilizes the eye""s signal processing system to provide an image that can be recognized by the subject. The invention may be applied to the eye(s) of a human or any other animal that has a similar visual system.
In one embodiment, the invention includes one or more carbon nanotube (CNT) towers, with each CNT tower including one or more CNTs, preferably multi-wall carbon nanotubes (MWCNTs). Each CNT tower has a first (exposed) end that penetrates the subject""s retina from a sub-retinal or epi-retinal location to a depth of 25-200 microns (xcexcm) and is located in a ganglion sub-layer or in a bipolar sub-layer (referred to collectively as the xe2x80x9cactivexe2x80x9d layer) of the retina, in order to transfer an electronic or electromagnetic signal from the CNT tower to the contiguous layer of the retina for subsequent signal processing by the subject""s eye. A second end of the CNT tower is connected through a metallic CNT growth catalyst (e.g., Fe, Ni, Co and/or Mo) and through a metallic underlayer or support layer (e.g., Al and/or Ir) to one or more of an array of light-receiving pixels in a photoreceptor array (e.g., a CCD pixel array). Each pixel has a preferred diameter of no more than about 50 nm, and preferably no larger than about 20 nm. The pixel array receives light that varies with pixel location on the array, and each pixel provides an electrical (electronic or electromagnetic) signal that is transferred through one or more CNT towers to the active layer of the retina. This system uses one or more CNT towers to transfer electrical signals from individual pixels in a pixel array to selected locations in an active layer of the retina.
In another embodiment, extension of neurite connections from the active layer of the retina to provide contact points for the CNT tower is encouraged, through chemical modification of, or provision of a selected coating of one or more proteins, growth factors and/or other biologically active substances on, a portion of the tower near the first end, or along the entire length of the tower.
In 1991, S. Iijima (Nature, vol. 354 pp. 56-58) reported growth of multi-wall coaxial nanotubes, containing 2-50 layers with radial separations of about 0.34 nm, using an arc discharge evaporation method similar to that used for Fullerene synthesis. The nanotubes originally observed by Iijima were formed on the negative voltage end of a carbon electrode and were plentiful in some regions and sparse in other regions. Since that time, other workers have developed other discharge means for controlled deposition of graphitic carbon.
Multi-wall carbon nanotubes (MWCNTs), single wall carbon nanotubes (SWCNTs) and carbon nanofibers (CNFs) have many potential applications that rely upon the large mechanical strength and/or large electrical conductivity associated with these structures, if the patterning of such structures can be controlled. Some workers have used liquid catalysts to initiate growth of some carbon nanotubes, but patterning of a finely detailed array of such structures is difficult using a liquid or a solid.
An array of CNTs can be grown by providing a substrate coated with an optional first thickness (preferably at least 1-10 nm) of a metal underlayer (e.g., Al or Ir or a mixture thereof) and with a second thickness (preferably at least 0.1-5 nm) of one or more active catalysts (e.g., Fe, Co, Ni and/or Mo, or a mixture thereof). A selected heated hydrocarbon gas (e.g., CH4, C2H4, and/or C2H2) or intermediate species (CmHn) is passed over the coated substrate to successively strip the H atoms and deposit the carbon particles on the catalyst. Optionally, the underlayer includes a first sub-underlayer and a second sub-underlayer with different materials. For an SWCNT array, the preferred gas is CH4 and the preferred temperature range is 800-1100xc2x0 C. (preferably, T≈900xc2x0 C.) For an MWCNT array, the preferred gas is C2H4 or C2H2, the preferred temperature range is 650-900xc2x0 C. (preferably, T≈750xc2x0 C.), and the Al or Ir underlayer is present. For a CNF array, a plasma discharge can be used to grow CNFs at T=400-900xc2x0 C. (preferably, T≈400-700xc2x0 C.). A selected pattern for the metal sub-layers on the substrate, or of catalyst on the substrate coated with the metal sub-layer, is formed, using an apertured mask, and the carbon nanotubes are grown in the selected pattern. Size of the pattern can be as small as 20 nm, if electron beam lithography or ion beam sputtering is used to define the pattern.